1. Field of the Invention
The present invention relates to electroluminescent devices employing single-ion conductors, more specifically, to organic/polymer electroluminescent devices employing single-ion conductors as an electron- or hole-injecting layer.
2. Description of the Related Art
Electroluminescent (“EL”) devices that emit light by applying an electric field to the device typically comprise an ITO (indium tin oxide) substrate, EL material and two electrodes. To improve the EL efficiency, the device is provided with a hole-injecting layer between the ITO electrode and EL material, an electron-injecting layer between EL material and the counter metal electrode, or both layers. As the EL material that plays a crucial role in the device, organic polymer/inorganic hybrid nanocomposite employing insulating inorganic materials, such as SiO2 and TiO2 that help the transport of electric charges, has been developed and put to the practical use (see: S. A. Carter, Applied Physics Letters, 71:1145, 1997; L. Gozano, Applied Physics Letters, 73:3911, 1998).
In the meantime, studies on the hole- or electron-injecting layer have been actively performed to improve the EL efficiency, mainly by way of inserting ionomers as the electron-injecting layer (see: Hyang-Mok Lee et al., Applied Physics Letters, 72, 2382, 1998). However, it cannot be a basic solution to improve the EL efficiency because the movement of ions is restricted in the ionomers, which naturally limits electron-injection. As an alternative means for efficient electron-injection, an electron-transporting layer rather than the electron-injecting layer, was proposed in the art, which utilizes the materials that well transport electrons and have high affinity to the electrons. Several methods that utilize inorganic nanoparticles, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), or metal chelate complexes have been presented until now (see: U.S. Pat. Nos. 5,537,000; 5,817,431; and 5,994,835). However, these methods have not been realized in practical use due to the low EL efficiency or the difficulties confronted in the thin film deposition process.
Under the circumstances, there are strong reasons for developing and exploring a material that can be used as the hole- or electron-injecting layer to improve the EL efficiency while employing the convenient thin-film deposition process such as a spin-coating method.